1. Field of the Invention
The present invention relates to a spindle motor and more specifically to a spindle motor used in a disk drive apparatus.
2. Description of the Related Art
Hard disk apparatuses and optical disk apparatuses are typically provided with a spindle motor to rotate a disk about a central axis. Such spindle motors include a stationary portion fixed to a housing of the apparatus, and a rotating portion arranged to rotate while supporting the disk. The spindle motor is arranged to produce a torque centered on the central axis by a magnetic flux generated between the stationary and rotating portions that works to rotate the rotating portion with respect to the stationary portion.
Some known spindle motors include a magnetic member arranged to attract the rotating portion toward the stationary portion. Such a magnetic member is typically fixed to the stationary portion to produce axial magnetic attraction between it and a magnet provided in the rotating portion. JP-A 2001-309605, for example, describes a conventional magnetic ring attached to a stationary member to apply a downward axial force to a rotor. JP-A 2007-43893, for example, also describes a conventional motor including a ring-shaped magnetic attraction ring fixed to a bottom surface of a motor base.
Concerning a method of fixing such a magnetic member to the stationary portion, paragraph [0034] of JP-A 2001-309605 includes the following explanation: “ . . . the magnetic ring 42 is adhered to the stationary member 21, for example, through an adhesive”. This adhesive, however, may deteriorate with a long-term use due to influence of changes in ambient temperature and the like which will result in a reduction in fixing strength of the adhesive. Since magnetic attraction constantly acts between the magnetic ring and the magnet, the deterioration of the adhesive may lead to a displacement of the magnetic ring toward the magnet. Therefore, the type of the adhesive and the amount of the adhesive applied need to be determined appropriately, with the long-term deterioration of the adhesive taken into consideration, to maintain a sufficient fixing strength of the adhesive.
Meanwhile, claim 1 of JP-A2007-43893 describes the following feature: “the attraction ring has a plurality of radially-projecting projecting portions defined in an outer circumferential portion or an inner circumferential portion thereof, and the projecting portions are press fitted to a wall portion provided in the motor base and arranged to project from the bottom surface thereof in an axial direction, so as to be fixed to the motor base”. The technique described in JP-A 2007-43893, however, has a problem in that a stress that accompanies the press fitting acts on the entire attraction ring. Therefore, the press fitting may lead to a deformation of the attraction ring as a whole. The deformation of the attraction ring results in variations in the axial distance between the magnet and the attraction ring. This may lead to contact between the magnet and the attraction ring, and the occurrence of undesirable vibrations due to uneven magnetic attraction, or the like.